The present invention relates to a phase shifter, and in particular, to a phase shifter for a microwave or millimeter wave band which is used as part of a phase control element of a phased array antenna etc.
A typical conventional switched line phase shifter is composed of two main lines, two or more switched lines (a reference line and one or more delay lines), and two or more RF (Radio Frequency) switches. Each end of a switched line is connected to one of the main lines through an RF switch. By the operation of the RF switches, the connection between the two main lines changes and thereby a desired phase shift is given to an RF signal which is passing through the phase shifter.
FIG. 1 is a circuit diagram showing a conventional switched line phase shifter. Referring to FIG. 1, the conventional switched line phase shifter includes two switched lines S and L and four RF switches SWaxcx9cSWd. Each switched line (S, L) is connected between two main lines ML1and ML2, and each RF switch (SWa, SWb, SWc, SWd) is connected between a main line and a switched line. The length of the switched line L is set longer than that of the switched line S. The connection between the main lines ML1 and ML2 through the switched line S or L is changed by the operation of the RF switches SWaxcx9cSWd. When the RF switches SWaxcx9cSWd, which operate together, are (OFF, OFF, ON, ON), the switched line L is connected with the main lines ML1 and ML2 and the switched line S is disconnected from the main lines ML1 and ML2 (hereafter referred to as xe2x80x9cstate Lxe2x80x9d). When the RF switches SWaxcx9cSWd are (ON, ON, OFF, OFF), the switched line S is connected with the main lines ML1 and ML2 and the switched line L is disconnected from the main lines ML1 and ML2 (hereafter referred to as xe2x80x9cstate Sxe2x80x9d). By the switching of the RF switches SWaxcx9cSWd between the states L and S, a phase shift corresponding to the length difference between the switched lines L and S is realized.
However, in the conventional switched line phase shifter which has been described above, phase shift deviation (deviation of phase shift when the frequency of an input RF signal varies) occurs as will be described below.
FIG. 2 is a plan view showing a conventional 90xc2x0 switched line phase shifter which is composed of microstrip lines, and FIG. 3 is an explanatory drawing which explains the operation of the conventional 90xc2x0 switched line phase shifter of FIG. 2 simply. FIGS. 2 and 3 are equivalent in electrical meanings. Referring to FIGS. 2 and 3, the lengths of the switched lines L and S are L=xcexg0/2 and S=xcexg0/4, therefore, the designed phase shift of the 90xc2x0 switched line phase shifter becomes xcex94"PHgr" 90xc2x0 corresponding to the length difference (Lxe2x88x92S=xcexg0/4) between the switched lines L and S.
FIG. 4 is a graph showing the phase shift deviation (phase shift-frequency relationship) of the conventional 90xc2x0 switched line phase shifter of FIGS. 2 and 3 (simulation result). In FIG. 4, the vertical axis denotes phase shift of the 90xc2x0 switched line phase shifter in the state S relative to the state L (xcex94"PHgr"="PHgr"Sxe2x88x92"PHgr")L ("PHgr"S:transmission phase delay in the state S, "PHgr"L: transmission phase delay in the state L)). Incidentally, a transmission phase delay of xc2xc xcexg0 is usually expressed as xe2x88x9290xc2x0 (negative), for example. The lengths (L, S) of the switched lines L and S are set based on the wavelength xcexg0 at the (designed) center frequency f0. For example, in the case of FIG. 3, the switched line lengths L and S are set so that Lxe2x88x92S will be xcexg0/4 (L=xcexg/2, S=xcexg0/4), thereby the phase difference between the states L and S becomes xcex94"PHgr"32 90xc2x0 at the center frequency f0.
However, in the frequency range higher than the center frequency f0, the wavelength is shorter than xcexg0 and thus the phase shift becomes larger than 90xc2x00 . On the other hand, in the lower frequency range, the wavelength is longer than xcexg0 and thus the phase shift becomes smaller than 90xc2x0 . Consequently, the phase shift-frequency relationship of the 90xc2x0 switched line phase shifter becomes a straight line having a positive slope as shown in FIG. 4. In the case of FIG. 4, the phase shift xcex94"PHgr" is precisely 90xc2x0 at the center frequency f0, however, the phase shift xcex94"PHgr" deviates from 90xc2x0 and the phase shift deviation becomes larger as the frequency of the input RF signal deviates from the center frequency f0.
Further, in the conventional switched line phase shifter which has been shown in FIGS. 1 through 3, four RF switches are necessary for switching the connections of the two switched lines L and S of different lengths and thereby obtaining the phase shift xcex94"PHgr". The number 4 of the RF switches is larger in comparison with other types of phase shifters. For example, a loaded line phase shifter can be implemented by only two RF switches.
It is therefore the primary object of the present invention to provide a phase shifter that can reduce the phase shift deviation and thereby enlarge the usable frequency range.
Another object of the present invention is to provide a phase shifter that can be implemented by a smaller number of RF switches.
In accordance with a first aspect of the present invention, there is provided a phase shifter for digitally shifting the phase of an RF (Radio Frequency) signal by changing a switched line which is connecting two main lines into another switched line. In the phase shifter, at least one of the switched lines is always connected to one of the main lines so as to operate as an open stub when the RF signal is not passed through the switched line.
In accordance with a second aspect of the present invention, in the first aspect, the phase shifter comprises a first main line, a second main line which is placed a predetermined distance apart from the first main line, a first switched line which is placed between the first main line and the second main line, a second switched line which is placed between the first main line and the second main line and which is always connected to the second main line, a first switch for controlling the connection/disconnection between the first main line and the first switched line, a second switch for controlling the connection/disconnection between the second main line and the first switched line, and a third switch for controlling the connection/disconnection between the first main line and the second switched line.
In accordance with a third aspect of the present invention, in the second aspect, the length of the first switched line is set to xc2xc of the wavelength of the RF signal and the length of the second switched line is set to xc2xd of the wavelength and thereby a 90xc2x0 phase shifter is implemented.
In accordance with a fourth aspect of the present invention, in the second aspect, the length of the first switched line is set to xc2xd of the wavelength of the RF signal and the length of the second switched line is set to the wavelength and thereby a 180xc2x0 phase shifter is implemented.
In accordance with a fifth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by microstrip lines.
In accordance with a sixth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by slot lines.
In accordance with a seventh aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by co-planer lines.
In accordance with an eighth aspect of the present invention, in the second aspect, the first main line, the second main line, the first switched line and the second switched line are implemented by coaxial lines.
In accordance with a ninth aspect of the present invention, in the second aspect, the first switch, the second switch and the third switch are implemented by PIN diodes.
In accordance with a tenth aspect of the present invention, in the second aspect, the first switch, the second switch and the third switch are implemented by FETs (Field-Effect Transistors).
In accordance with an eleventh aspect of the present invention, in the second aspect, the first switch, the second switch and the third switch are implemented by mechanical relays.
In accordance with a twelfth aspect of the present invention, in the second aspect, the first switch, the second switch and the third switch are implemented by micromachine switches.
In accordance with a thirteenth aspect of the present invention, in the second aspect, the first switch, the second switch and/or the third switch are installed in positions which are withdrawn from the main lines.
In accordance with a fourteenth aspect of the present invention, in the first aspect, the phase shifter comprises a first main line, a second main line which is placed a predetermined distance apart from the first main line, a switched line which is placed between the first main line and the second main line and which is always connected to the second main line, a first switch for controlling the connection/disconnection between the first main line and the second main line, and a second switch for controlling the connection/disconnection between the first main line and the switched line.
In accordance with a fifteenth aspect of the present invention, in the fourteenth aspect, the length of the switched line is set to xc2xd of the wavelength of the RF signal and thereby a 180xc2x0 phase shifter is implemented.
In accordance with a sixteenth aspect of the present invention, in the fourteenth aspect, the first main line, the second main line and the switched line are implemented by microstrip lines.
In accordance with a seventeenth aspect of the present invention, in the fourteenth aspect, the first main line, the second main line and the switched line are implemented by slot lines.
In accordance with an eighteenth aspect of the present invention, in the fourteenth aspect, the first main line, the second main line and the switched line are implemented by co-planer lines.
In accordance with a nineteenth aspect of the present invention, in the fourteenth aspect, the first main line, the second main line and the switched line are implemented by coaxial lines.
In accordance with a twentieth aspect of the present invention, in the fourteenth aspect, the first switch and the second switch are implemented by PIN diodes.
In accordance with a twenty-first aspect of the present invention, in the fourteenth aspect, the first switch and the second switch are implemented by FETs (Field-Effect Transistors).
In accordance with a twenty-second aspect of the present invention, in the fourteenth aspect, the first switch and the second switch are implemented by mechanical relays.
In accordance with a twenty-third aspect of the present invention, in the fourteenth aspect, the first switch and the second switch are implemented by micromachine switches.
In accordance with a twenty-fourth aspect of the present invention, in the fourteenth aspect, the first switch and/or the second switch are installed in positions which are withdrawn from the main lines.
In accordance with a twenty-fifth aspect of the present invention, in the first aspect, the phase shifter comprises a first main line, a second main line which is placed a predetermined distance apart from the first main line, a first switched line which is placed between the first main line and the second main line, a second switched line which is always connected to the first main line, a third switched line which is placed between the second switched line and the second main line and which is always connected to the second main line, a first switch for controlling the connection/disconnection between the first main line and the first switched line, a second switch for controlling the connection/disconnection between the second main line and the first switched line, and a third switch for controlling the connection/disconnection between the first switched line and the second switched line.
In accordance with a twenty-sixth aspect of the present invention, in the twenty-fifth aspect, the length of the first switched line is set to xc2xe of the wavelength of the RF signal and the lengths of the second switched line and the third switched line are set to xc2xd of the wavelength and thereby a 90xc2x0 phase shifter is implemented.
In accordance with a twenty-seventh aspect of the present invention, in the twenty-fifth aspect, the lengths of the first switched line, the second switched line and the third switched line are set to xc2xd of the wavelength of the RF signal and thereby a 180xc2x0 phase shifter is implemented.
In accordance with a twenty-eighth aspect of the present invention, in the twenty-fifth aspect, the first main line, the second main line, the first switched line, the second switched line and the third switched line are implemented by microstrip lines.
In accordance with a twenty-ninth aspect of the present invention, in the twenty-fifth aspect, the first main line, the second main line, the first switched line, the second switched line and the third switched line are implemented by slot lines.
In accordance with a thirtieth aspect of the present invention, in the twenty-fifth aspect, the first main line, the second main line, the first switched line, the second switched line and the third switched line are implemented by co-planer lines.
In accordance with a thirty-first aspect of the present invention, in the twenty-fifth aspect, the first main line, the second main line, the first switched line, the second switched line and the third switched line are implemented by coaxial lines.
In accordance with a thirty-second aspect of the present invention, in the twenty-fifth aspect, the first switch, the second switch and the third switch are implemented by PIN diodes.
In accordance with a thirty-third aspect of the present invention, in the twenty-fifth aspect, the first switch, the second switch and the third switch are implemented by FETs (Field-Effect Transistors).
In accordance with a thirty-fourth aspect of the present invention, in the twenty-fifth aspect, the first switch, the second switch and the third switch are implemented by mechanical relays.
In accordance with a thirty-fifth aspect of the present invention, in the twenty-fifth aspect, the first switch, the second switch and the third switch are implemented by micromachine switches.
In accordance with a thirty-sixth aspect of the present invention, in the twenty-fifth aspect, the first switch and/or the second switch are installed in positions which are withdrawn from the main lines.